1. Field of the Invention
The present invention relates to an openable and closable barrier device disposed in front of an optical system to protect the optical system.
2. Description of Related Art
A conventional barrier device disclosed, for example, in Japanese Laid-Open Patent Application No. Hei 7-159856 is composed of two barrier blades, a barrier driving ring, barrier springs, a barrier-driving-ring spring, and a connection shaft. The two barrier blades are arranged to cover the front of a photo-taking optical system. The barrier driving ring rotates around an optical axis of the photo-taking optical system to drive the barrier blades to open and close. Each of the barrier springs is mounted between the barrier blade and the barrier driving ring to constantly bring the barrier blade into contact with the barrier driving ring and to urge the barrier blade in the direction of closing, and absorbs a relief movement of the barrier driving ring relative to the barrier blade. The barrier-driving-ring spring is mounted between the barrier driving ring and a lens-barrel cover to urge the barrier driving ring counterclockwise and to drive the barrier blade in the direction of opening. The connection shaft is arranged to transmit the rotational movement of a rotating barrel (member) to the barrier driving ring.
Operation of the conventional barrier device configured as described above is briefly described. When the rotating barrel rotates clockwise, the rotational movement of the rotating barrel is transmitted to the barrier driving ring via the connection shaft. The barrier driving ring then rotates clockwise while charging the barrier-driving-ring spring, so that the barrier blades rotate counterclockwise following the rotation of the barrier driving ring. This rotation results in the barrier blades covering the front of the photo-taking optical system. On the other hand, when the rotating barrel rotates counterclockwise, a contact portion between the rotating barrel and the connection shaft comes into a free state. The barrier driving ring then rotates counterclockwise under the spring force of the barrier-driving-ring spring, which has been in the charged state, so that the barrier blades rotate clockwise following the rotation of the barrier driving ring. This rotation results in the barrier blades uncovering the front of the photo-taking optical system.
In cases where some obstacles (for example, foreign matter such as sand) prevent the barrier blades from rotating in the direction of closing in the process of closing operation, the barrier springs allow the barrier driving ring to rotate clockwise, while being charged by the clockwise rotation of the barrier driving ring. In other words, the barrier springs allow a relief movement of the barrier driving ring relative to the barrier blades. This leads to prevention of occurrence of any mechanical failure.
However, there are problems associated with the conventional barrier device as follows. The conventional barrier device necessitates an increased number of parts and a relatively high cost because dedicated parts for driving the barrier blades to open and close (i.e., the barrier driving ring and the barrier-driving-ring spring) and dedicated parts for absorbing a relief movement of the barrier driving ring relative to the barrier blades when some obstacles (for example, foreign matter such as sand) prevent the barrier blades from rotating in the direction of closing in the process of closing operation (i.e., the barrier springs) are required. In addition, the whole lens barrel increases in size because such dedicated parts require a relatively large configuration space.
Furthermore, there is another problem with the conventional barrier device in that, since both the barrier-driving-ring spring, which drives the barrier driving ring, and the barrier springs, which absorb a relief movement of the barrier driving ring relative to the barrier blades, are required, a load on operation of the lens barrel occurring at the time of the closing operation of the barrier blades increases, if these springs are configured with a balancing of spring forces taken into consideration in view of measures against possible obstacles.